Principle of Internal Combustion Engine
The principle behind any reciprocating internal combustion engine: If you put a tiny amount of high-energy fuel (like gasoline) in a small, enclosed space and ignite it, an incredible amount of energy is released in the form of expanding gas. You can use that energy to propel a potato 500 feet. In this case, the energy is translated into potato motion. You can also use it for more interesting purposes. For example, if you can create a cycle that allows you to set off explosions like this hundreds of times per minute, and if you can harness that energy in a useful way, what you have is the core of a car engine!
Almost all cars currently use what is called a four-stroke combustion cycle to convert gasoline into motion. The four-stroke approach is also known as the Otto cycle, in honor of Nikolaus Otto, who invented it in 1867. The four strokes are illustrated in Figure 1. They are:
The principle of working of both SI and CI engines are almost the same, except the process of the fuel combustion that occurs in both engines. In SI engines, the burning of fuel occurs by the spark generated by the spark plug located in the cylinder head. The fuel is compressed to high pressures and its combustion takes place at a constant volume. In CI engines the burning of the fuel occurs due to compression of the fuel to excessively high pressures which does not require any spark to initiate the ignition of fuel. In this case the combustion of fuel occurs at constant pressure.
Both SI and CI engines can work either on two-stroke or four stroke cycle. Both the cycles have been described below:
1) Four-stroke engine: In the four-stroke engine the cycle of operations of the engine are completed in four strokes of the piston inside the cylinder. The four strokes of the 4-stroke engine are: suction of fuel, compression of fuel, expansion or power stroke, and exhaust stroke. In 4-stroke engines the power is produced when piston performs expansion stroke. During four strokes of the engine two revolutions of the engine's crankshaft are produced.
2) Two-stroke engine: In case of the 2-stroke, the suction and compression strokes occur at the same time. Similarly, the expansion and exhaust strokes occur at the same time. Power is produced during the expansion stroke. When two strokes of the piston are completed, one revolution of the engine's crankshaft is produced.
In 4-stroke engines the engine burns fuel once for two rotations of the wheel, while in 2-stroke engine the fuel is burnt once for one rotation of the wheel. Hence the efficiency of 4-stroke engines is greater than the 2-stroke engines. However, the power produced by the 2-stroke engines is more than the 4-stroke engines.
The ignition of compressed air and fuel exerts a tremendous amount of force on the top of the piston, moving it downward in the cylinder. At this point, a few other components must be mentioned: the connecting rod and crankshaft. A connecting rod is attached to the inside of each piston. The bottom end of the rod connects to a section of the crankshaft. Crankshafts have numerous sections that are not in-line; some sections fall in the center-line, and others are offset. The offset sections are surrounded by the bottom ends of the connecting rods. When the piston is forced downward, the connecting rod moves with it. The rod forms a link between the piston and the crankshaft, yet the design of the crankshaft causes its motion to be rotary rather than up-and-down. The crankshaft rotates when the connecting rod applies force to it. A component called a flywheel (in vehicles with manual transmission) or a torque converter (in vehicles with automatic transmissions) is connected to one end of the crankshaft. This component is the connecting point between the vehicle's engine and drive train.
Once the piston has moved downward after combustion, the rotary motion of the crankshaft moves it back up the cylinder. At this time, the exhaust valve is opened and the leftover gas from combustion called exhaust is forced out of the chamber. Once this valve closes and the piston moves downward again, the intake valve opens and the partial vacuum created by the piston's downward motion pulls more mixture into the chamber. Valve timing is controlled by the camshaft, a component that is linked to the crankshaft. The camshaft turns as the crankshaft does, but at half the speed. It is composed of lobes, or egg-shaped knobs whose longer ends push on valves directly or on components linked to valves to open them. Once the lobe's long end comes off the valve or linked component, spring pressure returns the valve to its seated, closed position.
Internal combustion engines rely on the principles of compression, precise timing and proper mechanical functioning of all components involved. When these principles are present, a small spark leads to a force great enough to power a vehicle.
The principle behind any reciprocating internal combustion engine: If you put a tiny amount of high-energy fuel (like gasoline) in a small, enclosed space and ignite it, an incredible amount of energy is released in the form of expanding gas. You can use that energy to propel a potato 500 feet. In this case, the energy is translated into potato motion. You can also use it for more interesting purposes. For example, if you can create a cycle that allows you to set off explosions like this hundreds of times per minute, and if you can harness that energy in a useful way, what you have is the core of a car engine!
Almost all cars currently use what is called a four-stroke combustion cycle to convert gasoline into motion. The four-stroke approach is also known as the Otto cycle, in honor of Nikolaus Otto, who invented it in 1867. The four strokes are illustrated in Figure 1. They are:
- Intake stroke
- Compression stroke
- Combustion stroke
- Exhaust stroke
The principle of working of both SI and CI engines are almost the same, except the process of the fuel combustion that occurs in both engines. In SI engines, the burning of fuel occurs by the spark generated by the spark plug located in the cylinder head. The fuel is compressed to high pressures and its combustion takes place at a constant volume. In CI engines the burning of the fuel occurs due to compression of the fuel to excessively high pressures which does not require any spark to initiate the ignition of fuel. In this case the combustion of fuel occurs at constant pressure.
Both SI and CI engines can work either on two-stroke or four stroke cycle. Both the cycles have been described below:
1) Four-stroke engine: In the four-stroke engine the cycle of operations of the engine are completed in four strokes of the piston inside the cylinder. The four strokes of the 4-stroke engine are: suction of fuel, compression of fuel, expansion or power stroke, and exhaust stroke. In 4-stroke engines the power is produced when piston performs expansion stroke. During four strokes of the engine two revolutions of the engine's crankshaft are produced.
2) Two-stroke engine: In case of the 2-stroke, the suction and compression strokes occur at the same time. Similarly, the expansion and exhaust strokes occur at the same time. Power is produced during the expansion stroke. When two strokes of the piston are completed, one revolution of the engine's crankshaft is produced.
In 4-stroke engines the engine burns fuel once for two rotations of the wheel, while in 2-stroke engine the fuel is burnt once for one rotation of the wheel. Hence the efficiency of 4-stroke engines is greater than the 2-stroke engines. However, the power produced by the 2-stroke engines is more than the 4-stroke engines.
The ignition of compressed air and fuel exerts a tremendous amount of force on the top of the piston, moving it downward in the cylinder. At this point, a few other components must be mentioned: the connecting rod and crankshaft. A connecting rod is attached to the inside of each piston. The bottom end of the rod connects to a section of the crankshaft. Crankshafts have numerous sections that are not in-line; some sections fall in the center-line, and others are offset. The offset sections are surrounded by the bottom ends of the connecting rods. When the piston is forced downward, the connecting rod moves with it. The rod forms a link between the piston and the crankshaft, yet the design of the crankshaft causes its motion to be rotary rather than up-and-down. The crankshaft rotates when the connecting rod applies force to it. A component called a flywheel (in vehicles with manual transmission) or a torque converter (in vehicles with automatic transmissions) is connected to one end of the crankshaft. This component is the connecting point between the vehicle's engine and drive train.
Once the piston has moved downward after combustion, the rotary motion of the crankshaft moves it back up the cylinder. At this time, the exhaust valve is opened and the leftover gas from combustion called exhaust is forced out of the chamber. Once this valve closes and the piston moves downward again, the intake valve opens and the partial vacuum created by the piston's downward motion pulls more mixture into the chamber. Valve timing is controlled by the camshaft, a component that is linked to the crankshaft. The camshaft turns as the crankshaft does, but at half the speed. It is composed of lobes, or egg-shaped knobs whose longer ends push on valves directly or on components linked to valves to open them. Once the lobe's long end comes off the valve or linked component, spring pressure returns the valve to its seated, closed position.
When an internal combustion engine is first started, it requires a
starter motor to begin the motion. The motor turns the crankshaft, which
transfers its motion to the connecting rod and piston. The piston then
compresses the air and fuel mixture in the combustion chamber. Once
combustion has occurred, the force created thereby moves the crankshaft
through the connecting rod. The crankshaft's inertial motion works to
keep the piston moving up and down the cylinder, and the process of
combustion continues for as long as the vehicle is running.
Internal combustion engines rely on the principles of compression, precise timing and proper mechanical functioning of all components involved. When these principles are present, a small spark leads to a force great enough to power a vehicle.
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